A method has been developed which identifies a class of genes relatively important in neoplasia-predisposition in the general population and which measures the risk of malignant neoplasms for heterozygous carriers of each gene in this class. This method is based on autosomal recessive syndromes associated with cancer and leukemia. The heterozygous carriers of genes for each of these syndromes occur in the population at a frequency between 0.01 and 0.001, so that detecting a significant increase in risk of malignant neoplasm for the heterozygous carrier of any of these genes would imply that that gene is an important neoplasia-predisposing gene of man. An association between malignant neoplasms and each gene in this class can be detected by a retrospective study of the illnesses and causes of death in families with homozygous probands (affected with a particular autosomal recessive syndrome), since heterozygotes are frequent in such families. It is possible to measure the general risk of malignancy associated with each gene studied and to detect associations between specific types of malignant neoplasms and individual genes. These associations may provide useful leads for investigating the genetic basis of tumor induction in man by specific oncogenic agents. It may be possible to detect and analyze the effects of individual genes on life expectancy or in predisposing to diabetes mellitus by the same methods of data collection and analysis.